Rock-drill.



PATENTED JUNE 25, 1907.

J. B. MARSHALL.

ROCK DRILL.

nrmnnmx FILED DBO.13,1906.

INVENTOH JOHN B.MARSHALL ATTORNEYS WITNESSES (7, AM

TN; New: rsrzn; co, WASHINGTON. a c.

UNITED STATES PATENT OFFICE.

JOHN BRINKLEY MARSHALL, OF BROKEN HILL, NEW SOUTH WALES, AUSTRALIA.

ROCK-DRILL.

Specification of Letters Patent.

Patented June 25, 1907.

Application filed December 13,1905. Serial No. 291.549.

T0 at whom it may concern:

Be it known that I, JOHN BRINKLEY MAR- SHALL, engineer, a subject of the King of Great Britain and Ireland, residing at Broken Hill, State of New South Wales, Commonwealth of Australia, have invented a certain new and useful Improvement in Rock- Drills, for which the following is a specification.

This invention relates to rock drills of the Ingersoll type such as the Eclipse with sensitive spool valves.

It relates to the construction of the piston and is designed forthe purpose of reducing or eliminating the tendency to cushion the blow in such drills as hitherto constructed which cushioning reduces the drills efficiency. In drills of that type the valve is controlled in its action by a depressed or annular recessed part in the piston, that is a part turned down to a smaller diameter, which depressed part therefore acts in itself as a valve. The action of this is well known and is as follows The spool valve has four piston like surfaces, two internal and two external, all of which are capable of being affected by the pressure of the air or steam feed owing to the feed be ing admitted between the two ends and leaking past each end to the external surfaces of same. Motion is obtained by relieving this pressure from one of the two outside sur faces. This pressure is relieved by the action of the annular recess in the piston completing through suitable assages a communication between one o the relief outlets from the valve chest and the exhaust chamber of the drill. Owing to this annular recess being approximately the length of the span between the two relief ports and of uniform depth throughout there is a tendency for the valve to reverse with a very short traverse of the piston, hence the slightest movement of the piston beyond midstrokein either direction permits or causes the valve to reverse. The premature reversal of the valve by admitting air against the piston before the completion of its stroke cushions and partly neutralizes the force of the .blow.

According to my invention the recess is made in two portions and the depth of the same is varied to give a smaller escape for the air at the forward end of the piston, thus the front end of recess passing the front relief port does not permit sufficient escape to cause a sudden reversal of the valve nor does reversal occur until a deeper part of the recess encounters the relief port. At the same time by my method of construction there is adequate escape at all parts of the stroke for reversing when required.

- In order that my invention may be clearly understood I will describe the same with reference to the accompanying drawings, in which Figure 1 is a longitudinal section of a drill cylinder with my piston in place therein, and Fig. 2 is a bottom plan view of the valve chest.

The cylinder A is constructed in the ordinary manner and fitted with an ordinary valve chest B provided with suitable inlet and outlet ports I), Z), respectively and with an exhaust port 6 the ports being controlled by an ordinary valve 6 Since, however, the construction of the cylinder and the valve chest forms no part of my invention I have not deemed it necessary to further describe the same.

Within the cylinder operates the piston C, the said piston being provided with the usual rifle nut c in which operates the rifle bar 0 provided on its outer end with the ratchet wheel 0 with which cooperates the pawl c in the ordinary and well known manner. The annular recessed portion of the piston is made in two portions c of the same overall length as heretofore but instead of being of uniform depth throughout the portion 0 is made of the greatest depth at the back end and. tapers off forward until it reaches ap proximately the full diameter-of the piston a little short of the total length. The totallen th is com leted b a roovec of a similar depth to the depth of the portion 0 at its back end. The groove is for the purpose of insuring that the drill shall not fail to start on the outward stroke from the extreme inner position.

Having now fully described and ascertained my said invention and the manner in which it is to be performed I declare that what I claim is- 1. In a rock drill having a valve, a piston having an annular recess for controlling the operation of the valve, said recess comprising spaced annular grooves and a tapered portion connecting the grooves, whereby to 0p- 1 depth, being of greater depth toward the back end of the piston and tapering off toward the front end but with a deeper groove in advance of the shallower part and forming the immediate front end of-the recess substantially as described and illustrated and for the purpose set forth.

In a rock drill of the type specified, a

piston having an annular recess in two portions one portion at the forward end of the recess comprising a small groove of suitable depth and Width, and the other portion ex tending from the edge of such groove to the rear end of the recess and gradually increasing in depth from the edge of such groove to the rear end substantially as described and illustrated and for the purpose set forth.

In testimony that I claim the foregoing as my invention 1 have signed my name in the presence of two subscribing witnesses this second day of November 1905.

JOHN BRINKLEY MARSHALL.

\Vitnesses LnsLIE HER-BERT BROADBENT, ARTHUR GORE CoLLrsoN. 

